1. Field of the Invention
The subject invention is directed to nozzles that provide a controlled spray pattern and, more particularly, fuel nozzles for providing atomized fuel to a combustion chamber.
2. Description of the Prior Art
Various types of fuel nozzles are known in the prior art. For example, pressure atomizer nozzles produce a spray pattern by passing the fuel through an orifice under pressure. Another type of fuel nozzles is the prefilming type nozzle wherein the fuel is swirled in an annular passage before it is mixed with air. One example of this type of nozzle is shown in U.S. Pat. No. 3,980,233 to Simmons, et al.
Some recent applications for fuel nozzles require intermittent operation for spraying volumes of fuel that are relatively small in comparison to prior art applications. For example, in some recent applications, nozzles must operate at fuel flow rates approximately ten times less than flow rates typical for aircraft application.
Downsizing prior art nozzles to accommodate these lower fuel flow rates has presented a variety of problems. For example, the relatively small orifices of the downsized nozzles were difficult to make and were subject to being plugged with particulate contaminants in the fuel. Guarding the fuel orifices with low micron rated filters is costly and inconvenient due to the frequent servicing requirements.
Because of the low fuel flow requirements, merely increasing the size of the fuel orifices so that particulate contaminants would pass through the orifices, did not permit sufficient fuel velocity to produce an acceptable spray pattern. For example, under such conditions pressure atomizer type nozzles simply did not atomize. Prefilming air-blast nozzles did not prefilm the fuel, resulting in poor atomization and fuel distribution. Moreover, in some nozzles the angle of the spray pattern is partially dependent on the fuel flow rate. This decrease in fuel flow rate produces unacceptable changes in the spray pattern angle.
Accordingly, there was a need in the prior art for a smaller, reliable nozzle that would produce a desirable spray pattern at low fuel flow rates.